Ford Repair: Ford EEC-IV/V open loop at WOT ?, air fuel ratio, ford eec

Question
Hi Steve -

I hope this doesn't count as an "electrical question."  I have read and heard completely contradictory answers to the question - does the Ford EEC-IV in my 5.0L (Speed Density) Fox TBird or the EEC-V in my 4.6L (Mass Air) Mustang stay in closed loop during WOT, or go into open loop?  

If it goes into open loop (as so many tech articles state), why would it do that?  Why not continue to use O2 sensor feedback to control fuel metering?  Especially since the desired air-fuel ratio is different at WOT ...  And if it is not using O2 sensor feedback, how does the ECM determine fuel metering ?  ROM fuel maps based on vehicle speed, engine RPM, etc?  It just seems counter-intuitive.

I hope that you can straighten this out for me once and for all -- thanx.  

Answer
Chuck-

  Oh man...this is something I haven't brushed up on in a while, so I may be a bit rusty in my old age (said the 24 year old college student).  I *believe* that both systems go into open loop at WOT.  To someone programming EPROM memory like that found in the EECs, it's much easier to just assume that, at WOT, you've got a given amount of air (as much as the engine can handle) at a given rpm so therefore you need a given amount of gas and timing.  Most aftermarket engine control units require you to program WOT fuel enrichment, timing, etc. so I feel a bit safe in assuming that these things aren't controlled by the ECU to begin with.  I'm not entirely sure, but that's as best I can recall.  Hope this helps.

Steve